Flat sheet or film extrusion dies have been provided with various mechanical means for adjusting the die lip in order to provide a controlled film or sheet thickness. This has sometimes been accomplished by providing a flexible or slidable lip. It has been conventional to use a plurality of bolts spaced apart from each other along the lip to control the lip gap at a plurality of space points along the lip. Adjusting the individual lip bolts involves considerable skill, takes time and adds to the cost of production.
With sliding lips, damage can result to the lip and die body due to adjustment and/or interchanging of lips. Sliding lips are heavy and hard to handle, especially when heated. Many operators use "pry bars" to move the components which may cause damage.
Thermal expansion and contraction of lip-adjusting components may be used to adjust the lip opening, such as described in U.S. Pat. No. 3,940,221 to Nissel, U.S. Pat. No. 4,753,587 to Djordjevic, et al, and U.S. Pat. No. 5,208,047 to Cloeren, et al.
Certain conventional designs employ a movable upper lip portion along with a rigid or fixed lower lip portion. When the gap is adjusted by flexing an upper lip, a limited range of adjustment is possible, typically up to about 0.075 to 0.100 inches of adjustment. A sliding lip may be used to provide for a greater gap range; however, the adjustment or substitution of lips is time consuming. It is also difficult to measure the lip gap and then modify the gap by adjusting numerous bolts.
Convenient adjustment of the lip gap and accurate measurement of the adjustment are desired. However, convenient adjustability of the lip gap during extrusion is lacking in conventional designs, as is a convenient means for accurately measuring the gap.
Repeatable and precise adjustment are desired features. A smooth, non-jerking adjustment is beneficial. Repeatability at a later time would reduce set-up time.
An approach for adjusting the lip gap using an adjustable bottom lip, is illustrated by EP 668 143, published on Aug. 23, 1995, to Extrusion Dies, Inc. This approach uses a generally laterally movable angle block having one or more angled cam blocks extending therefrom, and a lip adjustment block coupled to the bottom lip and including one pr more angled grooves or recesses sized to closely receive the cam blocks for sliding movement therein. A threaded stud extends axially from one end of the angle block through a hole in an end plate and is received by a complementarily threaded spool. Rotation of the spool results in generally lateral movement of the angle block and in single point adjustment of the lip gap.
This approach is asserted to solve many problems of conventional dies. However, the lip adjustment block and the corresponding angle block are difficult to manufacture. Because the cam blocks of the angle block fit into the angled grooves of the block and the entire lengths must fit perfectly, accurate machining is required. This difficulty increases with increased length. Likewise, replacement and repair of these components is expensive and time consuming, and because of the interfit, it may be necessary to remove both components.
In addition, the lengths of the lip adjustment block and angle block cause other problems. A lengthy component may tend to warp, and because of thermal expansion and retraction, the possibility of warping is increased. Moreover, long pieces of sixty inches or more usually require greater machining clearance for the pieces to mate properly, which may result in non-uniformity along the die lip. Furthermore, rotation of the spool can be difficult if the long pieces do not properly fit and align. If so, costly oversized or special thread forms may be necessary.
The lip adjustment blocks are uncovered, and therefore molten material may flow onto the cam blocks and/or into the grooves of the lip adjustment block. As a result, interfit and/or movement of these parts may be hindered or prevented, and there may be greater stress, deformity, and opportunity for wear.
The lip adjustment blocks are secured by shoulder bolts to the die body. Elongated holes in the lip adjustment blocks permit movement of the blocks. When a block is adjusted, the head of the shoulder bolt experiences stress. The stress is focused on edges of the head and edges of the elongated holes, tending to wear the head and holes.
When used, externally attached deckles are attached to the movable lip adjustment blocks. However, because these blocks move up and down, interference with the deckle function and wear of the deckle and lip surfaces may result.
It is therefore an object of the present invention to provide an extrusion apparatus having single point adjustment for lip gap control across its full width, yet ease of manufacture.
It is a further object to provide an extrusion apparatus with an adjustable lip that moves smoothly, precisely, and with accurate repetition, and that provides for quick adjustments and does not interrupt the extrusion process.
It is a still further object to provide an extrusion apparatus with interfitting lip adjustment components that can be be easily interfit and move into alignment, easily manufactured, and are removable, interchangeable and replaceable.
It is an even further object to prevent material flow into and/or onto the lip adjustment components.
It is an additional object, when an external deckle is used, to mount the deckle so that movement of the lip adjustment components does not affect contact of the deckle with the exit slot.
It is another object to provide an extrusion apparatus having a single point adjustment for the lower lip and a single point adjustment for the upper lip.
It is yet another object to provide an improved method for profiling extruded flat sheet material.
Still further objects and advantages will become apparent from a consideration of the description and drawings.
In accordance with the invention, there is provided an extrusion apparatus including a flexible lip for adjusting the gap of the exit slot, a plurality of spaced apart, reciprocally movable members in operable contact with the flexible lip, and a generally laterally movable actuator bar connected with the reciprocally movable members by pin members. In accordance with the invention, the reciprocally movable members each include an angled slot, the actuator bar includes spaced apart bores, and the pin members include head portions engaged with the angled slots and shaft portions rotatably mounted in the actuator bar bores.
Also, there is provided an assembly for control of the reciprocally movable members and the actuator bar. The assembly beneficially includes a generally laterally disposed adjustment stud having an end engaged with the actuator bar and having a non-circular portion, and a locking member having a throughbore of a cross-sectional shape and size for preventing rotation of the adjustment stud.
In addition, in accordance with the invention, there is provided a method of profiling extruded flat sheet material using the foregoing extrusion apparatus. By the method, the lip gap is adjusted to a selected profile, and a material is extruded through the profiled lip gap. The lip gap profile is provided by at least one of the angled slots of other of the reciprocally movable members.